There exist current feedthroughs for outdoor electrical gear that are made of molded synthetic material. An example of such a feedthrough is shown in FIG. 1, said feedthrough comprising a central conductor 1 having insulating resin 2 overmolded thereon and including a molded fixing flange 3 of the same material. A field-controlling screen 4 is generally embedded in the resin between the flange and the conductor in the zone where the feedthrough is mounted in the opening provided for it in a wall 5 of the metal cladding of a piece of gear. The flange is fixed to the wall by bolts in a manner that is not shown herein, and it possesses an annular groove for a sealing gasket 6 enabling the feedthrough to be mounted on the wall in hermetically sealed manner. That type of feedthrough suffers from the drawbacks of using a material that is relatively fragile, of requiring the use of a gasket which is difficult to assemble, and of a field-controlling screen whose positioning is critical. In addition, the conical outside shape of the feedthrough in the stress zone that lies between the flange and the fins 7 is unsuitable for receiving a toroidal current transformer.
There also exist composite type feedthroughs, an example of which is shown in FIG. 2. Such a feedthrough has a core of molded resin 9 about a central conductor 8 and a fixing flange 10 that is integrally molded with the core. The outside surface of the flange and of a cylindrical portion 10A of the core immediately adjacent to the flange is covered in a conductive covering 11 that is designed to be grounded when the feedthrough is in place. The metal-covered cylindrical portion 10A is suitable for enabling at least one toroidal current transformer 12 to be installed thereon in the vicinity of the fixing flange. An electric field distributing cone 13 is threaded onto the core after the current transformer(s) and before a series of fins 14 of elastomer material which are stacked on the core one after the other. Functionally, the cone is equivalent to the conical stress zone included in the feedthrough shown in FIG. 1, and it serves to control the field at the end of the metal covering, overlying the cylindrical portion 10A and a portion of itself following said cylindrical portion when the feedthrough is assembled. The desired electrical creepage distance is obtained by means of the stack of fins 14 in a manner that is known to the person skilled in the art. This second type of feedthrough is fixed on the wall 15 of the metal cladding of piece of gear in the same manner as is the first type described above, and it requires the same type of sealing gasket to be installed, so it suffers from the same drawbacks in this respect. It also suffers from the drawback of using a relatively large number of different parts so that manufacture and assembly thereof gives rise to a succession of operations, and in particular of manual operations. Finally, if ever it is necessary to replace a toroidal transformer, e.g. following a failure, it is necessary to dismantle the fins and the electric field distributing cone.